Stone attempted to enter Parliament Buildings in November 2006 armed with explosives, knives and an axe.

He denied it had been a bid to kill the politicians, instead claiming it was an act of performance art.

In 2013 he was told that he must serve the remainder of a 30-year sentence for waging his sectarian murder campaign.

Stone's case has been referred to Parole Commissioners on the basis that he has now served the minimum term.

However, Ms McGuinness claimed the Department wrongly included the six years he spent out on licence before the attack on Stormont.

Her legal team contended that he should not be considered eligible for release until 2024 - when a full 30 years will have been served in custody.

Ronan Lavery QC said: "A period on licence cannot satisfy the requirements of retribution and deterrence, only a period in custody can do that."

Explaining the reasons behind the tariff imposed, counsel told the court Stone had been described as a "professional" who offered his services as a killer to any loyalist paramilitary group who would use him.

He had committed multiple murders designed to strike fear into the community, the two judges hearing the case were told.

"It's not just the ones that we all remember, the Stormont incident and the incident in which my client's brother was killed at Milltown Cemetery.

"There are other incidents, other individuals who were murdered and (subjected) to attempted murder."

Stone carrying out his attack at Milltown Cemetery in March 1988

The barrister argued that the Life Sentences (Northern Ireland) Order 2001 does not enable a period on licence to be included as part of the time served.

"We don't execute people in this country, but we sentence them to a prison sentence for life, and they are subject to that for life," he continued.

"The minimum term represents that period of the sentence which is punishment."

David Scoffield QC, representing Stone, rejected the case being made against his client.

"Where you are on licence a life prisoner is still serving a life sentence," he submitted.

Acknowledging Ms McGuinness's feelings, Mr Scoffield also said: "We recognise the concern that may well be caused to the applicant at the prospect of Mr Stone being released or, at this stage, simply seeking release.

"It's difficult not to have sympathy about her position, but this is a case about application of the law."